High temperature, solid oxide electrolyte fuel cells and multi-cell generators and configurations thereof designed for converting chemical energy into direct current electrical energy at temperatures typically in the range of 600.degree. C.-1200.degree. C. are well known and taught, for example, in my U.S. Pat. Nos. 4,395,468 (Isenberg) and 4,490,444 (Isenberg). A multi-cell generator generally contains a plurality of parallel, axially elongated, electrically connected electrochemical fuel cells, each fuel cell having an exterior fuel electrode, an interior air electrode, a solid oxide electrolyte sandwiched between the electrodes, and gaseous oxidant and gaseous hydrocarbon fuel entry means. The hydrocarbon fuel prior to contacting the fuel cell is reformed to hydrogen (H.sub.2) and carbon monoxide (CO) which is flowed parallel to the exterior surface of the fuel electrode. The reformed hydrocarbon fuel is electrochemically oxidized by an oxidant such as oxygen (O.sub.2) or air which is flowed over to the interior surface of the air electrode. Direct current electrical energy is generated. Exhaust gases such as a portion of the spent fuel are combusted together with spent oxidant in a combustion chamber and vented as hot combusted exhaust gas. Another portion of the spent fuel is recirculated and combined with fresh hydrocarbon feed fuel to provide the oxygen species for hydrocarbon reformation and conditioning of the hydrocarbon feed fuel for electrical power generation reaction. Reformation of the incoming hydrocarbon feed fuel can be performed either inside or outside of the generator, although an internal reformer is preferred since reformation reactions are endothermic and are performed at a temperature close to that of the electrochemical fuel cell operation, typically between 600.degree. C.-1200.degree. C., and excess heat from the fuel cell generator can be usefully transferred to the reformer.
Natural gases comprising mostly methane (CH.sub.4), with additions of ethane (C.sub.2 H.sub.6), propane (C.sub.3 H.sub.8), butane (C.sub.4 H.sub.10) and the like, vaporized petroleum fractions such as naphtha and the like, and also alcohols, such as ethyl alcohol (C.sub.2 H.sub.5 OH) and the like, are appropriate oxidizable fuels for electrochemical reactions, and can be consumed in an electrochemical generator apparatus for generating electrical power, such as a high temperature, solid oxide electrolyte. However, the direct use of hydrocarbon fuels for generating electrical power can cause carbon deposition and soot formation on the fuel cells and other generator components at least partly from hydrocarbon cracking. Deposition of carbon on the generator components tends to damage and/or interfere with proper generator operations. Carbon can cause, inter alia, blocking of porous electrodes, create electrical shorts between electrodes, reduce insulation effectiveness, block, poison and mechanically destroy reformation catalysts, such as nickel supported on alumina in pellet form. Elimination of carbon deposition, therefore, requires conditioning of the hydrocarbon feed fuel gases by hydrocarbon reformation to noncarbonizing gas mixtures such as CO and H.sub.2 together with CO.sub.2 and H.sub.2 O, as the fuel for the fuel cells.
In the known high temperature, solid oxide electrolyte, fuel cell generators, the hydrocarbon feed fuel gas, such as natural gas, is generally mixed with H.sub.2 O (steam) and/or CO.sub.2, typically supplied from recirculated spent fuel gas comprising at least H.sub.2 O and CO.sub.2, and is passed together with hydrocarbon feed gases through an internal hydrocarbon reformer containing a packed bed of nickel (Ni) catalyst pellets at elevated temperatures typically at 500.degree. to 700.degree. C., to produce reformed fuel gas of H.sub.2 and CO to be fed to the fuel electrode of the fuel cell. These conventional reformation catalysts have a limited life in that they tend to be deactivated. They are then discarded. The discarded catalyst must be replaced to continue to supply conditioned fuel to the fuel cell, which creates downtime and stops electrical power generation operations.
U.S. Pat. No. 5,143,800 (George, et all.) discloses a high temperature, solid oxide electrolyte, electrochemical fuel cell generator having a conventional internal hydrocarbon reformer containing a packed bed of Ni reforming catalyst supported on alumina pellets. The reforming catalyst consists of fine metal which is supported on aluminum oxide as catalyst carrier, this is the preferred catalyst in hydrocarbon reformation. The reformer chamber is an elongated circular vessel having an annulus to provide recuperative heat transfer from the combusted exhaust gas exit channel and the spent fuel gas recirculation channel. In George, et al., a portion of spent fuel comprising at least H.sub.2 O and also typically CO.sub.2, H.sub.2 and CO, is recirculated and combined with incoming fresh hydrocarbon feed fuel gas via a mixing nozzle in order to provide a homogeneous, reformable gas mixture which thereafter is fed through the reforming chamber containing the nickel catalyst pellet bed. In the presence of water vapor and carbon dioxide, and in contact with the reforming catalyst, the reformation of a gaseous hydrocarbon, for instance methane (CH.sub.4) can proceed via the following reaction shown in Equation (1). ##STR1##
In George, et al., the reforming chamber is characterized in that the incoming fresh hydrocarbon feed fuel gas has one or more by-pass channels controlled by valves so that the fresh hydrocarbon feed fuel can by-pass the aspirating portion and flow directly into the gaseous spent fuel recirculation channel, to control the amount of spent fuel gas (oxygen species) recirculated into the aspirator, in order to assure an appropriate O:C ratio or H.sub.2 O: gaseous hydrocarbon ratio is achieved under various operating conditions. U.S. Pat. No. 4,898,792 (Singh, et al.) discloses other typical hydrocarbon reforming catalyst materials used to condition the hydrocarbon fuels fed to a high temperature, solid oxide electrolyte fuel cell generator, such as Ni plus oxides of Mg, Ca, Al, Sr, Ce, or Ba and mixtures thereof. As described above, these catalysts have drawbacks in that they have a limited life and need be replaced, during electrical power generation operations.
It would be advantageous however to provide a hydrocarbon reformer, for example in a high temperature, solid oxide electrolyte, electrochemical fuel cell generator (SOFC), which continuously supplies a reformed fuel to the fuel cell generator and which is continually regenerated and reactivated during its lifetime in order to match the lifetime of a SOFC fuel cell generator (approx. 50,000 hours or more). It would also be advantageous to provide a reforming catalyst material for an internal hydrocarbon reformer of an electrochemical fuel cell generator which stores and supplies all the oxygen species for the hydrocarbon reformation reaction in order to eliminate the need for additional steam generation for the reformation process. The reforming medium in such a system of the invention is a mixture of iron oxide (FeO), and iron (Fe) and the system of the invention is characterized by a swing bed-reformation process having alternating iron metal and iron oxide beds (Fe/FeO).
In the swing bed-reformation process and apparatus of the invention, at least two Fe/FeO beds are used. One bed is mainly in the iron oxide (FeO) condition and incoming hydrocarbon feed fuel gas, such as natural gas, will be reformed to CO and H.sub.2 which represents the fuel to be fed to the fuel cells, whereby FeO is reduced to Fe metal. While this FeO reformer bed is being reduced to Fe, the other Fe/FeO bed which previously served as a reformer bed is reoxidized from its mainly Fe-form to a mainly FeO-form with generator spent fuel gases. When the iron oxide of the FeO active reformer bed is substantially depleted of oxygen for reformation, the hydrocarbon fuel feed gas together with some spent fuel gas is switched over to the other bed which consists now mostly of FeO. This bed is now the active fuel reformer bed while the other one is reoxidized to be ready for another switch over. However, during reactivation with spent fuel gas this bed also produces some fuel (H.sub.2 and CO).